It is well-known that from the time the green coffee beans are roasted they generate and release gasses, such as carbon dioxide and, to a lesser degree, carbon monoxide, in a process known as “off-gassing.” Over time, off-gassing of packed coffee can cause an increase in the internal pressure of a hermetically sealed coffee container. To negate this increase in internal pressure, coffee containers have historically been constructed of rigid materials, such as metals, and are subjected to vacuum before sealing. Indeed, until recently, if a consumer purchased roast and ground coffee, the most common option available was a metal coffee can. And while metal coffee cans generally remain sealed, thereby keeping the coffee inside fresh, such containers are not without problems. For example, metal coffee cans often add to the purchase price of the product since producing the metal cans can be costly, and because the cans must be packed under vacuum. Another concern with metal cans is that when the cans are filled with coffee, they are heavy and may be difficult to handle for those suffering from hand, arm or joint conditions, such as arthritis.
As a way to address some of the foregoing concerns with metal coffee cans, manufacturers have recently begun making semi-rigid roast and ground coffee containers. Such containers are constructed from materials other than metal. One alternative is constructing the container from a plastic, such as a polyolefin. See U.S. patent application Ser. No. 10/155,338. Making the container from plastic reduces the cost of manufacturing and shipping the product, and also increases the ease of handling by reducing the weight of the product, and allowing for easy-to-grip handles to be molded into the container.
In spite of these advantages, semi-rigid containers are still not without issues. It has been discovered that if the semi-rigid container is vacuum packed similar to metal cans, the container has a tendency to collapse or distort. This distortion often leads to failure of the closure seal of the container. To remedy this problem, the coffee is often degassed prior to packing. Degassing involves storing the freshly roasted coffee in holding bins for extended periods of time, known as the “hold time,” prior to packing. This hold time allows the off-gasses generated to evolve and dissipate. Often, degassing takes several days. By degassing the coffee, the problem of internal pressure build-up and closure seal failure is reduced. However, closure failure may also arise when transporting the semi-rigid containers through changes in altitude and temperature because such environmental changes also affect the release of off-gases from coffee and thus, the pressure exerted on the container. These environmental changes in pressure are known as pressure differentials. Due to the flexible nature of the containers, pressure differentials may also result in the containers contorting or collapsing. Again, this can damage the closure seal and allow atmospheric oxygen into the container, which can stale the coffee.
It has been discovered that one way to account for pressure differentials is to place a one-way valve in the closure of the container as described in U.S. application Ser. No. 10/155,338. Placing a valve in the closure eliminates the need for hold time, since off-gasses evolving after packaging are released through the valve. Additionally, such a valve aptly accounts for pressure differentials as the packed coffee is transported through differing altitudes and temperatures.
However, placing a one-way valve in the closure of the container also has its attendant problems. When shipping such containers over increasing elevations, these valves continue to release off-gasses in order to equilibrate with the decreasing atmospheric pressures. As the elevation decreases, the container is subject to continuously increasing atmospheric pressure to which the container cannot equilibrate, due to one-way valve now being closed. This increase in atmospheric pressure compresses the container and pushes down on the seal to form a dish like appearance. Such ‘dishing’ exposes the seal area of the container to high stress which can cause closure failure, and consequently, staling of the coffee. Often, additional plastic must be used to reinforce the seal area of the container to account for this increase in seal stress.
Additionally the off-gases that escape from the containers via one-way valves can fill the empty parts of the enclosed shipping trailer, thereby reducing oxygen levels to undesirably low levels.
Therefore it is desirable to devise a way to package freshly roasted coffee in hermetically sealed containers such that the one-way valve is no longer required, yet the closure seal remains intact, and the product remains fresh.